In modern window cleaning systems, washer fluid pumps of said type are often mounted on a washer fluid container and are known from practice. The ventilation opening serves for acclimatization and pressure equalization of the housing which has the electromotive drive, and in the known washer fluid pumps, is usually embodied as an open end of a ventilation duct which leads straight through the housing. Here, the ventilation opening must be large enough to permit an infiltration of air into the housing and out of the housing. An excessively small ventilation opening tends to become blocked, which often leads to a pressure build-up and to damage of sealing elements between the electromotive drive and the pump unit. An excessively small ventilation opening therefore leads to failure of the washer fluid pump. In addition, in the event of leakage of the pump unit, liquid must be discharged through the ventilation opening in order to avoid corrosion in the electromotive drive. An excessively large ventilation opening, however, leads to an infiltration of spray water and therefore to corrosion in the electromotive drive. Corrosion of said type likewise leads to failure of the washer fluid pump.